How long would it take to fully charge my Mac from 0 to 100% with my 5 W charger?

Why this question? Well, I have a cheap Chinese power bank that “claims” a battery capacity of 10,000 mAh. Uh, sure?

chinese-power-bank

OK maybe it’s not 10,000 mAh. Quit lying!

And the manufacturer didn’t lie only about the battery capacity - they lied about the capability as well. It says 5 V 2 A output on the bottom, but with my USB tester it only supplies 5.1 V at 0.95 A - which is about 5 W if rounded up.

So that was what piqued my question - how long would it take for my laptop to fully charge off of this?

Pull up the MacBook Pro 15” 2018 spec sheet, and you get this:

Built-in 83.6-watt-hour lithium-polymer battery

Ugh. Watt hours. Thankfully we can figure out the mAh rating if we know the voltage of the battery, and iFixit has done the hard work for us: 11.4 V. Now I don’t have to disassemble my Mac.

83.6 * 1000 / 11.4 = 7,300 mAh, give or take. Don’t like math? Use a calculator!

So this power bank can charge my laptop completely once, and partially after that? Doubt. But we want to see how long it would take.

7,300 mAh / 1,000 mA = 7.3 hours. Make it 8 hours, because you also need to consider efficiency and charging is not a perfectly efficient process.

…I think I’ll just stick to my Korean USB-C PD power bank instead.